1. Field of the Invention
The present invention relates to a magnetic recording and reproduction apparatus for recording on and reproducing a video signal from a magnetic tape. More particularly, it relates to a magnetic recording and reproduction apparatus having a video signal recording characteristic correction function capable of recording the video signal in an optimal recording state by testing a characteristic of a magnetic tape and adjusting a recording characteristic according to the tested characteristic.
2. Discussion of the Related Art
Since a video signal which is input to a magnetic recording and reproduction apparatus, such as a video tape recorder (VTR), has a frequency band of 30 Hz to 4.2 MHz, it is difficult to directly record the video signal on a magnetic tape. Therefore, the magnetic recording and reproduction apparatus modulates the input video signal to alter the frequency band of the video signal. Modulation methods, such as amplitude modulation (AM), frequency modulation (FM) and phase modulation, have been used to modulate the input video signal.
The magnetic recording and reproduction apparatus mainly uses a method for frequency-modulating the an input video signal's luminance signal that is appropriate to the magnetic recording channel. The input video signal's chroma signal is converted to a low frequency band, and then mixed with the frequency-modulated luminance signal to be recorded on the magnetic tape.
Since the chroma signal is recorded on the tape in a state of being mixed with the luminance signal, it is similar to a BIAS recording in which the chroma signal frequency becomes small and the luminance signal frequency becomes large. When the mixed signal is recorded on and reproduced from the tape, the luminance and chroma signals are recorded together with an interference component involving third-order distortion.
The interference component involving third-order distortion degrades the picture quality of a reproduced image. The interference component is represented as YC.sup.2 SIN(.omega.y-2 .omega.c)t, in which Y is the magnitude of a luminance carrier signal, C is the magnitude of a chroma carrier signal, .omega.y is an angular frequency of the luminance carrier signal and o)c is an angular frequency of the chroma carrier signal, and t is time. The interference component is demodulated along with the luminance signal component, and appears on a screen in the form of dot interference having an angular frequency of 2 .omega.c. Such interference is commonly called cross beat.
In the meanwhile, magnetic tapes have large characteristic deviations due to a difference in magnetic force, and are classified into several grades of tape performance based on the characteristic deviations. Also, heads contribute to characteristic deviation by more than approximately 30%, according to the head's structure and magnetic materials.
As described above, magnetic characteristics of the magnetic tape vary even within a specified range for a standard magnetic recording and reproduction apparatus. Accordingly, there is a drawback in that a video signal can not be properly recorded to comply with the characteristic of the tape.